Optical reflective measurement is one of the essential applications of optical analysis. With study of the optical properties of an analyte, people may detect the surface structure, measure the composition of the analyte, or quantify the concentration of a specific compound. The measurement of reflectance provides a remote, contactless, and non-invasive way to extract information from an analyte. Thus, the optical reflective measurement devices are widely used in analytical chemistry, aerospace, and medical fields. A light source, such as laser, is suitable for the applications. However, the instability of the light source and the wavelength dependent characteristics of beam splitter confine precision and accuracy of optical reflective measurement. The instability of the light source includes both the center wavelength drifting and the intensity noise. Also, inhomogeneity of the thin film coating and diffraction of the beam splitter contributes to the non-linear relationship between wavelength and transmittance (or reflectance). The noise resulted from the instability of the light source and the wavelength dependent characteristics of beam splitter hampers the acquisition of fine signals. As a result, the detected signals cannot represent the actual optical power of the reflected light beam.
Current technology has various approaches to improve the performance of such optical devices. First, the stability of the light may be improved by an advanced laser with designs of resonance cavity, laser control circuits, or laser optics, but this approach greatly increase the expense and form factors of the optical reflective measurement device. Second, anti-reflection coating of a beam splitter may mildly reduce diffraction, but still doesn't meet the strict requirement of measurement. Third, people may try to enlarge sample size to increase the statistical power of measurement, but larger sample size needs longer measurement duration or more measurement cycles. Furthermore, non-realtime measurement may not be able to acquire useful signals from many kinds of analytes or under mobile use. For example, some fluidic analyte may be inhomogeneous and flowing, such as vitreous humor in eye or blood in vivo. The present disclosure provides a solution to those technical problems, and the examples are described but not limited to these examples without departing from the scope of disclosure.